1. Field of Invention
The invention relates to microwave intrusion detectors. It has particular utility in dual detector systems that include a light emitting diode for indicating a single detector alarm.
2. Description of the Prior Art
Many technologies are employed for detecting intrusion. Microwave and infrared devices are examples frequently used together in dual technology systems. Both devices are aimed at the same region under surveillance and detection by both devices is required for a system alarm. Dual detection reduces false alarms even when both detectors are set to a higher sensitivity than would be practical operating alone.
Typical installations of dual detector systems are based on separate channels under a common control. One channel includes an active microwave device and associated amplifiers, filters and signal processing. The other channel includes a passive infrared device with components corresponding to those in the microwave channel. Both channels are monitored by logic in the common control. Although a single channel detection might be reported, a system alarm is initiated only when both devices detect an intrusion.
Light emitting diodes (LEDs) in several colors often are energized to indicate single and dual channel detection. One color represents the microwave channel, another color the infrared channel, and a third color the combined channels. Frequently the LEDs are placed on the detector where they are visible from the region under surveillance.